A cable, such as an electric cable comprising at least one electrical conductor, has to be bendable to be wound in coils onto a cable drum, e.g. after manufacturing and for transporting the cable to an installation site. When suspended between suspension points, due to gravity acting on the cable, the cable will bend at, and between, the suspension points. To permit this bending or flexing of the cable, a relative movement between an outer portion and an inner portion of the cable in the longitudinal directions is allowed. For some cable types the relative movement between the inner and outer portions may be in the order of magnitude of 0-10 mm, or even larger in certain regions along the cable.
A self-supporting cable is designed to support forces related to its own weight and preferably also external forces affecting the self-supporting cable, such as wind and falling trees. At least one conductor in an inner portion of the self-supporting cable or at least one messenger wire in the inner portion of the self-supporting cable is designed to bear these forces. A conductor may comprise one or several wires that are made out of aluminium and/or copper. One solution is therefore to let the conductor itself act as the supporting element. At a suspension point of a self-supporting cable, forces acting on the self-supporting cable are transferred via a suspension arrangement to a carrying structure for the self-supporting cable, typically some kind of pole. Various kinds of suspension arrangements are known. Some kinds of suspension arrangements engage with an exterior surface of the self-supporting cable and thus, the forces have to be transferred between an outer portion comprising the exterior surface and the inner portion of the self-supporting cable.
WO 2012/005638 discloses a self-supporting cable comprising an intermediate layer arranged between an outer portion and an inner portion of the self-supporting cable. Relative movement between the inner and outer portions is permitted. At a suspension point, where the self-supporting cable is subjected to radial forces from a suspension arrangement, the intermediate layer provides a frictional engagement between the inner and outer portions, by means of which forces acting along the self-supporting cable may be transferred between the inner and outer portions.
WO 2012/005641 discloses a similar self-supporting cable as WO 2012/005638.
U.S. Pat. No. 6,288,339 discloses a self-supporting cable comprising an outer jacket, an insulated conductor, and arranged therebetween attached, a shield band. An inner surface of the jacket, the shield band, as well as an outer surface of the insulated conductor is provided with undulations. This solution has the effect that the layers can slip relative to each other to some extent when the cable is bent.
When, in response to inwardly directed radial forces, such as applied from a suspension arrangement provided at suspension ends of the cable in the form of a spiral extending around and along a portion of the outer jacket of the cable of U.S. Pat. No. 6,288,339, the undulated layers cam into each other whereby slippage between the outer jacket and the insulated conductor is avoided. However, the undulations, in particular on the inner side of the jacket, may rupture under high load. This may in particular occur during high ambient temperature conditions, such as around 50° C. or above. As undulations start to rupture in such a high load region of the self-supporting cable, the loading force may be transferred to adjacent undulations, which adjacent undulations in turn may rupture. The grip between the outer jacket and the shield band is lost in the portions or regions of the cable where the undulations have ruptured. Eventually, an undesirable slippage between the outer jacket and the inner insulated conductor may occur. Such slippage could lead to the entire outer jacket rupturing and the suspension arrangement in the form of a spiral to unwind from the outer jacket of the self-supporting cable.